Direct hydrogen peroxide production using staged hydrogen addition

ABSTRACT

An improved catalytic process for producing hydrogen peroxide directly by reaction of hydrogen and oxygen is disclosed. The process employs staged or sequential feeding of portions of the hydrogen feedstream into zones in the catalytic reactor in amounts sufficient to maintain an essentially constant and preferred ratio of oxygen to hydrogen at the inlet to each of the vessel&#39;s zones whereby high selectivity for hydrogen peroxide production is achieved and excess oxygen recycle requirements are minimized.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of copending U.S. application Ser.No. 10/401,351, filed Mar. 28, 2003, pending, the disclosure of which isincorporated in its entirety.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The invention relates to an improved catalytic process for producinghydrogen peroxide directly by reaction of hydrogen and oxygen. Theprocess involves sequentially staged or serial feeding of portions ofthe hydrogen feed stream to the continuous catalytic reactor downstreamfrom the initial locus of the feedstream entrance to the reactor. Thestaged addition of hydrogen allows preferred oxygen to hydrogenstoichiometry to be maintained throughout the reactor. Thissignificantly reduces the amount of unconverted oxygen, thereby reducingor eliminating the need for recompression and recycling of effluentgases while improving the selectivity of the catalytic reaction.

2. Related Technology

While the direct production of hydrogen peroxide (H₂O₂) from hydrogen(H₂) and oxygen (O₂) is known in the art, commercial processes aretypically indirect processes using a hydrogen donor organic compound asthe source of hydrogen needed to react with oxygen in order tocircumvent the explosive hazard of direct mixtures of hydrogen andoxygen. Usually, anthraquinone or a derivative thereof is employed as ahydrogen donor molecule by first reducing the molecule to the dihydromoiety and then oxidizing the reduced dihydro moiety with oxygen toyield hydrogen peroxide and the starting anthraquinone. While arelatively safe process, the indirect process has many drawbacks, notthe least of which is the fact that it is a multi-step process whichconsumes anthraquinone and solvent by oxidation.

The direct catalytic production of hydrogen peroxide from hydrogen andoxygen, although well-studied, has not achieved commercial acceptance asyet. When the direct process is carried out at hydrogen levels below 5%by volume to avoid the explosive hydrogen gas mixture range, the yieldsof hydrogen peroxide are low. Further, the process selectivity is low asa consequence of the conversion of hydrogen peroxide to water in thecatalytic environment. The cost of hydrogen and oxygen is an importanteconomic factor in the direct synthesis process. Inefficiencies in theiruse caused by low selectivity constitute a significant problem.

Another significant economic problem in direct hydrogen peroxideproduction arises from the use of large gas excesses. It is commonpractice in direct synthesis processes to employ large excesses of oneof the gaseous components, especially oxygen. Consequently, large gasflows must be handled in the process. Since direct synthesis processestypically operate at pressures of at least 500 psig, and often greaterthan 1000 psig, the copious amount of excess oxygen in the reactionmixture which must be recompressed for recycle imposes a significantcost burden on the process. Large and expensive compressors are requiredto accommodate the recycle stream from direct synthesis processes thatemploy excessively large oxygen flows.

It is also well known in the prior art that the ratio of oxygen andhydrogen gases in the direct catalytic synthesis process has a criticaleffect on the yield of hydrogen peroxide produced as well as theselectivity of the process for hydrogen peroxide production. U.S. Pat.No. 4,336,239 teaches a direct synthesis hydrogen peroxide productionprocess using noble metal catalysts where the molar ratio of oxygen tohydrogen is greater than about 3.4, preferably above 5, and mostpreferably a molar ratio of 12–15, at catalyst loadings of more than 30mg per 100 ml of medium. According to the '239 patent, higher oxygen tohydrogen ratios above 3.4 result in an increase in the amount ofhydrogen peroxide obtained.

U.S. Pat. No. 6,375,920 teaches a reactor system for hydrogen peroxideproduction wherein hydrogen is fed to the reactor in staged points ofentry above an oxygen and hydrogen inlet. The process is distinguishedby employing a woven catalyst having a long on-stream life in a fixedbed reactor which produces a selectivity of above 65%. The '920 patentdoes not teach or claim the adjustment of the oxygen to hydrogen gasratio at each stage to provide a preferred ratio that yields a minimumvolume of a recycle stream.

U.S. Pat. No. 6,447,743 teaches a method for preparing hydrogen peroxidedirectly using staged oxygen addition into the reactor at a relativelyhigh ratio of oxygen to hydrogen.

U.S. Pat. No. 5,641,467 to Huckins teaches and claims a method for safehydrogen peroxide production in a catalytic reactor by injecting oxygenor oxygen and hydrogen into a flowing medium at multiple pointsdownstream in a catalytic reactor. The volumetric ratios of flowingmedium to injected hydrogen and/or oxygen are selected to preferablymaintain a safe combination of hydrogen to oxygen, or where the volumeratio of oxygen to hydrogen is from 1:1 to 20:1. However, the '467patent does not teach or claim the staged injection of hydrogen atvarying hydrogen to oxygen ratios that are pre-selected to maximize theconversion and selectivity of hydrogen peroxide production whileproducing low oxygen recycle ratios.

U.S. Pat. No. 6,042,804 is related to the foregoing '467 patent andteaches and claims the separation of hydrogen peroxide plus processoperating conditions within the explosive limits of hydrogen gas andoxygen mixtures.

It is an objective of the present invention to provide a process for thedirect continuous synthesis of hydrogen peroxide from hydrogen andoxygen gas in a catalytic reactor that avoids the necessity of feeding alarge excess of oxygen that might result in a substantial recycle streamof unconverted oxygen. It is a further objective of the invention toprovide such a process that avoids the production of and need forrecycling a large excess of oxygen but, nevertheless, achieves improvedprocess conversion of hydrogen and oxygen to hydrogen peroxide with highselectivity.

BRIEF SUMMARY OF THE INVENTION

The invention describes an improved process for the production ofhydrogen peroxide by the direct reaction of oxygen and hydrogen. Thegoverning principle of the invention is the fact that the performance ofthe direct synthesis process is significantly improved in terms ofprocess selectivity and conversion when the oxygen concentration in thedirect synthesis feed stream is higher than at least 50 weight percent,preferably at least 70 weight percent. Additionally, performance isimproved when the oxygen to hydrogen molar ratio is preferably greaterthan a value of about 1.5 or, more preferably, greater than 3. However,these preferred values of oxygen concentration and oxygen to hydrogenmolar ratio, when employing other processes, typically require the useof excesses of oxygen feed, and therefore lead to effluent gas flowscontaining large amounts of oxygen which must be recompressed andrecycled to the process at a significant economic penalty.

The hydrogen peroxide process of the present invention allows theoverall hydrogen and oxygen feeds to the direct synthesis reactor to bemaintained at or near the desired stoichiometric molar ratio ofapproximately 1:1, which eliminates the need for large excesses ofoxygen. This is achieved while distributing the oxygen and hydrogenfeedstreams to the reactor in a manner that maintains the desiredminimum concentration of oxygen in the reactor for hydrogen peroxideproduction while maintaining the desired molar ratio of oxygen tohydrogen in most or the entire continuous reactor. As a result, highvalues of selectivity and yield of hydrogen peroxide are realized in theprocess of the invention without experiencing the production of largeexcesses of unconverted oxygen that would otherwise requirerecompression with large compressors and recycling of large quantitiesof oxygen to the direct synthesis reactor. The objects of the inventionare realized by a staged addition of hydrogen to a multi-zoned reactorwhere portions of the hydrogen fed to the reactor are injected at pointsdownstream of the reactor first inlet.

More particularly, the invention comprises a multizoned or multistageddirect catalytic process for the production of hydrogen peroxide fromhydrogen and oxygen feedstreams wherein catalyst, preferably indecreasing amounts, is loaded into serially connected catalystconversion zones in a catalytic reactor. The zones comprise a first zoneand at least one receivably connected intermediate or terminal zonemaintained under conditions sufficient to convert hydrogen and oxygen tohydrogen peroxide. Most or all of an oxygen feedstream and a majorportion of a hydrogen feedstream are passed into the first conversionzone at an inlet molar ratio of oxygen to hydrogen between 1.5 and 10.Sequentially decreasing portions of the remaining fresh hydrogen feedstream are passed to the inlet of each of the receivably connectedserial intermediate or terminal conversion zones at a zone inlet molarratio of oxygen to hydrogen the same as that employed in the first zoneinlet. Hydrogen peroxide and unconverted hydrogen and oxygen arerecovered from the terminal zone effluent. Optionally, the unconvertedoxygen and hydrogen from the terminal zone effluent are recycled orsufficient quantities of hydrogen and oxygen are utilized in a singlepass process that obviates the necessity of recycling the reactor'sgaseous effluent. Notably, the molar ratio of oxygen to hydrogen in thecombined total of oxygen and hydrogen feedstreams is less than the inletmolar ratio of oxygen to hydrogen introduced into each of the conversionzones.

Preferably, most of the oxygen plus a portion of the hydrogen feedstreamand a liquid media feedstream in a molar ratio of oxygento-hydrogen-between 1.5 and 10 are introduced into the firstcatalyst-containing stage of the staged catalytic reactor. Hydrogen isfed into the downstream feed stream containing hydrogen peroxide,unconverted oxygen and hydrogen in all subsequent catalyst-containingstages in an amount sufficient to reestablish the molar ratio of oxygento hydrogen at the inlet of each stage to substantially correspond tothe molar ratio established at the first stage inlet. More particularly,additional amounts of hydrogen are fed into the second and subsequentcatalyst-containing stages along with effluent from the previous stage.

The multizoned or multistaged direct catalytic process of the inventionincludes at least one reactor with serially connected conversion zonesof successively decreasing size. In one embodiment of the invention, thereactor is of the fixed bed or ebullated bed type, and the seriallyconnected zones of the reactor each contain successively decreasingamounts of catalyst, either immobilized as a fixed bed or agitated as anebullated bed. In another embodiment, the reactor is of the slurry orfluidized bed type, where the liquid/solid slurry of reaction liquid andcatalyst passes through a series of reactor zones of successivelydecreasing volume. For the fixed bed reactor, the size of each zone isdefined by the amount of catalyst loaded into that zone. For theslurry/fluidized bed reactor, the catalyst is dispersed and travelsalong with the liquid phase. The size of each zone is determined by thereactor volume which, in turn, determines how long the liquid/solidmixture stays in each zone.

DESCRIPTION OF THE DRAWINGS

The FIGURE is a drawing depicting an example of a staged catalyticreactor vessel of the invention for the direct production of hydrogenperoxide.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a process for the production of hydrogenperoxide by direct synthesis from oxygen and hydrogen that avoids theuse of a large excess of one gas reactant and provides a means toachieve high selectivity. It has been found that high selectivity ofhydrogen peroxide production can be achieved if the direct synthesis iscarried out using an overall gas composition where the oxygenconcentration is at least 50% by volume of the total gas feed, andpreferably at least 70%. It has also been determined that highselectivity for hydrogen peroxide production can be achieved bymaintaining an oxygen-to-hydrogen ratio, molar or volume, of at least 2to 1, and preferably at least 3 to 1 in the reactor.

While excess oxygen is preferred in the process in order to achieve highselectivity for hydrogen peroxide production, in either or both of theabove cases the significant amount of excess oxygen used must berecovered and recycled in the process to maintain an economicallyfeasible process. But the cost of oxygen recycle is itself a seriouseconomic liability for the process because the amount of oxygen to berecycled dictates the use of large and expensive compressors.

The present invention provides a means to operate a continuous directhydrogen peroxide synthesis process under the foregoing preferredprocess conditions of overall oxygen concentration in the reactor andthe preferred ratios of oxygen to hydrogen while avoiding the need for asignificant excess of oxygen in the overall rector feed. The process ofthe invention provides a substantially diminished requirement in termsof the volume of the oxygen recycle stream and, consequently, the sizeof the required recycle compressors. In one preferred embodiment, theprocess of the invention can completely eliminate the need for recyclingof unconverted gases. These advantages are realized by carrying out thecontinuous direct synthesis of hydrogen peroxide in a catalytic reactorwhere the hydrogen gas that is fed to the reactor overall is injectedserially in diminishing discrete stages along the reactor length. Theamount of catalyst in each stage decreases from the first to the laststage of hydrogen gas injection corresponding to the decrease in theamount of hydrogen gas injected or fed at each stage. The amount ofhydrogen injected at each stage is held to an amount sufficient toestablish essentially the same ratio of oxygen to hydrogen at the locusof inject for all stages. Preferably, the ratio of oxygen to hydrogenfor all stages taken at their inlet hydrogen feed position is a constantselected from 1.5 to 10, but more preferably from 2 to 4.

Referring to the FIGURE, one schematic example of the reactor vesseluseful in the process of the invention is presented. The reactor shell 2contains multiple ports of feed entry including inlet 3 for feeding mostor all of the oxygen and inlet ports 4, 5 and n for introducinghydrogen. An essentially inert media feed may be introduced into thebottom of the reactor at 6 and product collected as an overhead stream7.

One key characteristic of the reactor is that there is little or noback-mixing of the gas flow throughout the reactor vessel. The reactorhas an essentially plug flow configuration with respect to the gas flow,whereas the liquid flow may be plug flow or back mixed. Anothercharacteristic of the process of the invention is that most or all ofthe oxygen-containing feed, which may be oxygen, air, enriched air, orany other oxygen-containing gas, is fed to the first stage of thereactor, i.e., the first inlet to the reactor. Yet anotherdistinguishing characteristic of the process of the invention is thatthe hydrogen feed is divided into multiple fractions, only one of whichis fed at the reactor entrance along with all of the oxygen-containinggas. The remainder of the hydrogen feed is injected in decreasingamounts at the subsequent downstream stages of the reactor. The numberof stages in the reactor may be arbitrarily selected, but it ispreferable to provide at least two hydrogen feed injection points plusthe first injection point where all of the oxygen feed plus a majorportion of the hydrogen gas feed is injected. Although larger numbers ofinjection points can be used to provide very uniform gas compositions,excessive numbers will make the reactor design needlessly complicated.In practice, it is preferred to use no more than 6 injection points.

Each stage of the reactor vessel contains catalyst, preferably supportednoble metal catalyst particles, preferably in decreasing amountsprogressing from the first stage to the terminal or last stage whereinthe amount of catalyst in any one stage corresponds approximately to thetotal quantity of oxygen and hydrogen present at the inlet of thespecific stage. The ratio of oxygen to hydrogen at the inlet of eachstage is predetermined to be constant or the same for each stage,although it is recognized that the ratio of oxygen to hydrogen withineach stage will rise sequentially as the reactants linearly traverseeach stage of the reactor. However, the hydrogen addition that iscarried out at each stage is in an amount sufficient to adjust or lowerthe oxygen to hydrogen ratio to the preferred consistent ratio. Thehydrogen feed may be divided into equal fractions or unequal fractionsand the injection points may be equally spaced or unequally spacedwithout departing from the requirement of the invention for maintainingthe oxygen to hydrogen ratio at the same preferred ratio at the inlet ofeach successive stage.

A particularly useful aspect of the present invention is the fact thatthe process of the invention avoids the requirement of many hydrogenperoxide processes of the prior art to execute the process at stagedhydrogen additions simply to assure that the process operates below theflammability or explosive limits of hydrogen. The process of the presentinvention is not limited to any such requirement. The process may runwithin the explosive limits of hydrogen or outside those limits.

The preferred gas composition ranges of the invention are selectedaccording to a completely different set of criteria than those imposedby the prior art relating to hydrogen peroxide production. It has beenfound that the process of the present invention can continuously produceextremely high selectivity for hydrogen peroxide production exceeding80% and even exceeding 90% selectivity when the process is carried underthe conditions described herein. This benefit is not anticipated in theprior art.

A preferred embodiment of the subject invention is one where the overallhydrogen and oxygen feed rates to the reactor are close to thestoichiometric ratio required for the reaction to produce hydrogenperoxide. In cases of high hydrogen peroxide selectivity, the desiredratio of oxygen to hydrogen is approximately 1:1. However, in caseswhere the overall selectivity is less than 100%, the actualstoichiometry of the reaction corresponds to lower oxygen to hydrogenratios. This is because the non-selective side reaction of hydrogen andoxygen to form water consumes less oxygen that the desired reaction toform hydrogen peroxide.

Another preferred embodiment of the process of the invention is onewhere the process is operated at a high per pass conversion of thegaseous reactants. The preferred conversion of hydrogen should be atleast 70%, and more preferably at least 80%. In the case where theoverall oxygen-to-hydrogen ratio is close to the actual stoichiometry,the per pass oxygen conversions is similarly high. The advantage of thisembodiment is that most of the gas feeds are utilized in a once-throughgas flow mode. This reduces or even eliminates the need forrecompression and recycling of the effluent gas and achieves significantcapital and operating cost savings.

In a particularly advantageous embodiment of the invention, the directsynthesis reaction is conducted using the Pd/C catalysts as described ineither applicant's U.S. Pat. No. 6,168,775 B1 or in pending U.S. patentapplication Ser. No. 10/205,881, filed Jul. 26, 2002, now abandoned.Both the '775 U.S. patent and the Ser. No. 10/205,881 patent applicationare incorporated herein by reference for all that they teach and claimof catalysts useful in the process of the instant invention. Very highselectivity levels can be achieved using the '775 catalyst in theprocess of this invention. However, the present invention may beconducted using any direct synthesis catalyst.

An especially preferred mode for the subject invention is one where thereactor operation and multiple hydrogen feeds are arranged to providefor a relatively uniform oxygen-to-hydrogen ratio throughout thereactor. It is well-known in the literature that the O₂:H₂ ratio exertsan important role in the selectivity and productivity of catalysts forthe direct synthesis of hydrogen peroxide from hydrogen and oxygen. Inparticular, it is known that ratios of greater than 1.5:1 are preferred,and ratios of more than 3:1 are more preferred. However, no prior artprocess provides a reactor that maintains a uniform distribution ofoxygen-hydrogen ratios, while also avoiding the need for substantial andcostly excesses of oxygen to maintain the preferred ratio.

In the preferred mode of the subject invention, a relatively uniformprofile of O₂:H₂ ratios are maintained across the reactor by subdividingthe reactor into a series of zones as described herein. While the zonesmay be of equal size, they are preferably designed to be of unequalsize. In the case where the reactor is of the fixed bed type, each zonewill be a section of packed catalyst wherein the “size” of the differentsections is defined by the amount of catalyst packed in each section.

To the first reactor zone, most or essentially all of the oxygen is fed,as well as all of the liquid feed to the reactor, but only part of thehydrogen. Additional parts of the hydrogen feed are then fed at pointsintermediate between the ensuing reactor zones until the last portion ofhydrogen is fed just upstream of the final reactor zone.

Where the sizes of the reactor zones differ, the amount of hydrogen fedto each bed will also differ, although not necessarily in exactproportion to the sizes of the reaction zones. The key aspect is thatthe scheme for subdividing the hydrogen feed is predicated on achievingthe desired uniform profile of oxygen/hydrogen ratio throughout thereactor.

While other arrangements are also possible, a further aspect of thepreferred mode of the invention is that the differing-sized reactorzones will preferably be arranged in order of decreasing size, with thelargest reactor zone placed at the inlet part of the reactor and thesmallest located at the exit. Correspondingly, the part of hydrogen feedto the first reactor section will be largest, and that to the last bedwill be the smallest.

The following examples are provided to illustrate the process of theinvention as well as the utility of the invention.

EXAMPLE 1

A catalyst containing 0.75% Pd on a carbon support packed into a fixedbed reactor where the reactor subdivided into 4 zones or bedsconstituting stages in the process of the invention. The reactor sarranged for cocurrent upflow of liquid and gas streams. The first bedis located at the bottom of the reactor and the last bed is located atthe top of the reactor. A total of 1667 kg of catalyst is charged tothis reactor across the four zones. The total amount of catalyst and thehydrogen feed are subdivided between the stages according to:

Hydrogen Feed Catalyst Section Catalyst Amount (kg) (kg-mol/hr) 1(Inlet) 764 250 2 474 114 3 271  59 4 (Outlet) 158  32 Total 1667  454

To the inlet of the first bed is fed 111,794 kg/hr of a liquid feedmixture comprised of methanol with 1% H₂SO₄ and 5 ppm NaBr. Also fed tothe first reactor is 531 kg-mol/hr of oxygen, which corresponds to anoverall O₂:H₂ feed ratio of 1.17, or only 17% excess oxygen. The reactoris operated at a total pressure of 27.5 bar (˜400 psia). Cooling isadjusted to maintain an average temperature of 45° C.

The following results are achieved:

Hydrogen Section Inlet Section Outlet Reactor Conversion O₂:H₂ ratioO₂:H₂ ratio H₂O₂ Produced Section (%) (molar) (molar) (kg/hr) 1 75 2.135.66 5730 2 66 2.01 4.06 3553 3 56 2.04 3.44 2036 4 46 2.14 3.15 1183Overall 90 — — 12,503

Based on hydrogen converted, the overall hydrogen peroxide selectivityis 90%. Based on hydrogen fed, the overall hydrogen peroxide yield is81%. Based on total oxygen fed, the overall hydrogen peroxide yield is69%. The product solution contains 10% hydrogen peroxide by weight. Theexample shows that with the present invention, a minimum O₂:H₂ ratio of2 can be maintained while only feeding a 17% excess of oxygen on anoverall basis.

EXAMPLE 2

A catalyst containing 0.75% Pd on a carbon support is packed into afixed bed reactor where the reactor is subdivided into 4 zones or bedsdefining stages. The reactor is arranged for cocurrent upflow of liquidand gas streams, so that the first bed is located at the bottom of thereactor and the last bed is located at the top. A cooling medium iscirculated through the shell of the reactor. A total of 1664 kg ofcatalyst is charged overall to this reactor with the catalyst amountsubdivided between the sections according to:

Hydrogen Feed Catalyst Section Catalyst Amount (kg) (kg-mol/hr) 1(Inlet) 689 211 2 458 116 3 306  77 4 (Outlet) 212  50 Total 1664  454

To the inlet of the first bed is fed 111,624 kg/hr of a liquid feedmixture comprised of methanol with 1% H₂SO₄ and 5 ppm NaBr. Also fed tothe first reactor section is 636 kg-mol/hr of oxygen, which correspondsto an overall O₂:H₂ feed ratio of 1.4, or only 40% excess oxygen. Thereactor is operated at a total pressure of 27.5 bar (˜400 psia). Coolingis adjusted to maintain an average temperature of 45° C.

This leads to the following performance results:

Hydrogen Section Inlet Section Outlet Reactor Conversion O₂:H₂ ratioO₂:H₂ ratio H₂O₂ Produced Section (%) (molar) (molar) (kg/hr) 1 80 3.0111.2 5168 2 71 3.01 8.04 3432 3 61 3.00 6.20 2296 4 53 3.04 5.39 1588Overall 90 — — 12,484

Based on hydrogen converted, the overall hydrogen peroxide selectivityis 90%. Based on hydrogen fed, the overall hydrogen peroxide yield is81%. Based on total oxygen fed, the overall hydrogen peroxide yield is58%. The product solution contains 10% hydrogen peroxide by weight. Thisexample shows that with the present invention, a minimum O₂:H₂ ratio of3 can be maintained while only feeding a 40% excess of oxygen on anoverall basis.

EXAMPLE 3

A catalyst containing 0.75% Pd on a carbon support is packed into afixed bed reactor, where the reactor is subdivided into 4 zones or beds.The reactor is arranged for cocurrent upflow of liquid and gas streams,so that the first bed is located at the bottom of the reactor, and thelast bed is located at the top. A total of 1655 kg of catalyst ischarged to this reactor with the catalyst amount subdivided between thesections according to:

Hydrogen Feed Catalyst Section Catalyst Amount (kg) (kg-mol/hr) 1(Inlet) 635 190 2 455 118 3 324  85 4 (Outlet) 241  61 Total 1655  454

To the inlet of the first bed is fed 110,979 kg/hr of a liquid feedmixture comprised of methanol with 1% H₂SO₄ and 5 ppm NaBr. Also fed tothe first reactor section is 758 kg-mol/hr of oxygen, which correspondsto an overall O₂:H₂ feed ratio of 1.67, or only 67% excess oxygen. Thereactor is operated at a total pressure of 27.5 bar (˜400 psia). Coolingis adjusted to maintain an average temperature of 45° C.

This leads to the following performance results:

Hydrogen Section Inlet Section Outlet Reactor Conversion O₂:H₂ ratioO₂:H₂ ratio H₂O₂ Produced Section (%) (molar) (molar) (kg/hr) 1 82 4.0017.9 4762 2 73 4.00 12.2 3410 3 63 4.00 9.19 2431 4 55 4.00 7.71 1809Overall 90 — — 12,412

Based on hydrogen converted, the overall hydrogen peroxide selectivityis 90%. Based on hydrogen fed, the overall hydrogen peroxide yield is81%. Based on total oxygen fed, the overall hydrogen peroxide yield is48%. The product solution contains 10% hydrogen peroxide by weight. Thisexample shows that with the present invention, a minimum O₂:H₂ ratio of4 can be maintained while only feeding a 67% excess of oxygen on anoverall basis.

The process of the invention lends itself well to the use of a varietyof reactor types and configurations known to those skilled in the art.As noted herein before, staged reactors are known in the art and can beapplied to fixed catalyst bed reactors, fluid bed reactors, ebullatedcatalyst bed reactors, catalyst slurry bed reactors, and the like. Thesereactors are applicable as well to the process of the invention. Theymay be configured in a variety of ways known in the art such as asingle, vertical reactor shell containing multiple zones or stagescontaining individual beds of catalyst particles and individual inletports to admit hydrogen feed. Optionally, each zone may comprise aseparate reactor shell connected to receive the feedstream from apreceding stage and designed to discharge an effluent to the next stage.The choice as to whether the reactor(s) are installed as a single ormultiple vertical reactor installation or a train of horizontal vesselsis the artisan's option.

Any catalyst known to those skilled in the art of hydrogen peroxideproduction may be used in the process of the Invention. However, it iswell known that supported noble metal catalyst particles, particularlypalladium on carbon support, are preferred as the catalyst for directhydrogen peroxide production from oxygen and hydrogen gases. Anespecially useful catalyst is the supported palladium catalyst preparedby the process described in the previously mentioned U.S. Pat. No.6,168,775. The catalysts described in that patent are useful for theprocess of this invention.

The amount of catalyst used in each zone of the process of the inventionis determined by consideration of a variety of variables includingreactor type and size, catalyst activity and life, and the feedstreamrate to each zone. Since most or all of the oxygen feed and a majorportion of the hydrogen feed are introduced into the reactor in thefirst stage, that stage will typically hold the preponderant share ofcatalyst particles.

A carrier liquid is preferably included as part of the total feedstreamto the first zone of the reactor of the process of the invention toassist in partly dissolving the reactants and propelling the feedstreamand products through the reactor. Preferred carrier liquids includewater, organic solvents, and mixtures thereof. In cases where thepreferred carrier includes, at least in part, an organic solvent, thepreferred solvents are alcohols such as methanol.

Reaction conditions that are useful for the process of the inventioninclude a temperature of 0° to 150° C. and a pressure from 1 bar to 100bar (15 psia to 1500 psia). The more preferred reaction conditionsinclude a temperature of about 30° to 45° C. at a pressure of 1 bar to70 bar (15 psia to 1050 psia). The amount of catalyst used in each zoneof the multistaged reactor vessel of the process of the invention may bethe same quantity for each stage, or the quantity may vary for eachstage. Most preferably, the hydrogen feed to each stage of the processdeclines from the first to the last stage as the oxygen feed that is fedto the first stage declines in concentration in subsequent stages as itis converted to hydrogen peroxide. Accordingly, the amount of catalystin each successive stage may be reduced in approximate proportion to thefeed rate of hydrogen gas into the particular stage. The amount ofcatalyst will also depend on the type of catalytic vessel beingemployed, i.e., fixed bed, ebullated bed, etc., and the activity of thecatalyst. These variables are well understood by artisans in the fieldwho can select the amount of catalyst in each stage sufficient tooptimally satisfy the variables. In the most preferred case, thecatalyst will comprise palladium on a carbon support for all stages,with the catalyst optionally containing a minor amount of platinum inaddition to the palladium.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A method for the direct catalytic conversion of hydrogen and oxygento hydrogen peroxide employing a multi-stage reactor operated underconditions so as to convert hydrogen and oxygen to hydrogen peroxide inthe presence of a catalyst, the method comprising: introducing afeedstream comprising oxygen, hydrogen and a liquid media into an inletof a first stage of the multi-stage reactor in order to establish aninitial molar ratio of oxygen to hydrogen of at least about 1.5 at thefirst stage inlet; passing an effluent from the first stage of themulti-stage reactor into one or more subsequent stages downstream fromthe first stage, the effluent having a molar ratio of oxygen to hydrogenthat is less than the initial molar ratio; introducing a supplementalfeed comprising mostly or entirely hydrogen into the effluent in anamount so as to reestablish a molar ratio of oxygen to hydrogen in eachsubsequent stage that is at least initially closer to the molar ratioestablished at the first stage inlet than that of the effluent from apreceding stage; and recovering hydrogen peroxide and unconverted oxygenand hydrogen, the unconverted oxygen and hydrogen having a molar ratioof oxygen to hydrogen that is less than the molar ratio established atthe first stage inlet of the multi-stage reactor, the molar ratio ofoxygen to hydrogen within each stage of the multi-stage reactorexceeding the overall molar feed ratio of oxygen to hydrogen utilizedthroughout the method.
 2. A method as defined in claim 1, wherein themulti-stage reactor is selected from the group consisting of a fixed bedreactor system comprising serially connected fixed catalyst beds, anebullated bed reactor system comprising serially connected ebullatedcatalyst beds, and a slurry bed reactor system comprising seriallyconnected slurry catalyst beds.
 3. A method as defined in claim 1,wherein the oxygen has a concentration of at least about 50% by weightof the feedstream.
 4. A method as defined in claim 1, wherein the oxygenhas a concentration of at least about 70% by weight of the feedstream.5. A method as defined in claim 1, said liquid media comprising at leastone of water or an organic solvent.
 6. A method as defined in claim 5,said liquid media comprising a mixture of water and alcohol.
 7. A methodas defined in claim 1, wherein the molar ratio of oxygen to hydrogenestablished at the first stage inlet is at least about
 3. 8. A method asdefined in claim 1, wherein an overall feed ratio of oxygen to hydrogenutilized throughout the method is from about 1 to about 1.67.
 9. Amethod as defined in claim 1, wherein the method utilizes a supportednoble metal catalyst comprising at least one of palladium or platinum.10. A method as defined in claim 9, wherein the supported noble metalcatalyst comprises catalyst particles having crystal faces in an orderlylinear arrangement characteristic of the 110 and/or 220 exposition. 11.A method as defined in claim 1, the multi-stage reactor being operatedat a temperature between about 0° C. to about 100° C. and a pressurebetween about 1 bar to about 100 bar.
 12. A direct catalytic method forthe production of hydrogen peroxide from hydrogen and oxygen,comprising: maintaining a reactor containing a catalyst in seriallyconnected catalytic conversion zones of successively decreasing volumeunder conditions sufficient to convert hydrogen and oxygen to hydrogenperoxide, said conversion zones comprising a first conversion zonereceivably connected to receive most or all of an oxygen feedstream anda portion of a hydrogen feedstream and one or more subsequent conversionzones receivably connected to receive a remaining portion of thehydrogen feedstream and a remaining portion, if any, of the oxygenfeedstream, wherein the molar ratio of oxygen to hydrogen utilizedthroughout the method is less than the molar ratio of oxygen to hydrogenintroduced into each of the conversion zones; introducing most or all ofthe oxygen feedstream and a portion of the hydrogen feedstream into thefirst conversion zone of the reactor at an initial molar ratio of oxygento hydrogen of at least about 1.5; passing an effluent from the firstconversion zone of the reactor into one or more downstream conversionzones, the effluent having a molar ratio of oxygen to hydrogen that isless than the initial molar ratio; introducing sequentially decreasingamounts of a remaining portion of the hydrogen feedstream into each ofthe one or more subsequent conversion zones in order to reestablish aninitial molar ratio of oxygen to hydrogen in each subsequent subsequentconversion zone that is closer to that introduced into the firstconversion zone than that of the effluent from a preceding conversionzone; and recovering hydrogen peroxide and any unconverted hydrogen andoxygen from a terminal conversion zone effluent. the molar ratio ofoxygen to hydrogen within each stage of the multi-stage reactorexceeding the overall molar feed ratio of oxygen to hydrogen utilizedthroughout the method.
 13. A method as defined in claim 12, wherein themolar ratio of oxygen to hydrogen introduced into the first conversionzone is at least about
 3. 14. A method as defined in claim 12, whereinthe overall feed ratio of oxygen to hydrogen utilized throughout themethod is from about 1 to about 1.67.
 15. A direct catalytic method forconverting hydrogen and oxygen to hydrogen peroxide employing amulti-stage reactor operated under conditions so as to convert hydrogenand oxygen to hydrogen peroxide in the presence of a catalyst, themethod compnsing: introducing a feedstream comprising oxygen, hydrogenand a liquid media into a first catalyst-containing stage of themulti-stage catalytic reactor at an initial molar ratio of oxygen tohydrogen of at least about 1.5; maintaining the firstcatalyst-containing stage under conditions sufficient to converthydrogen and oxygen to hydrogen peroxide as the feedstream is fedtherethrough; introducing supplemental hydrogen into a downstreamfeedstream near an inlet of one or more sequential catalyst-containingstages to lower the molar ratio of oxygen to hydrogen in the downstreamfeedstream to a ratio that is closer to the initial molar ratio, whereinessentially no supplemental oxygen is introduced into the one or moresequential catalyst-containing stages such that the overall molar ratioof oxygen to hydrogen in the combined reactor inlet streams is less thanthe molar ratio at the inlet of the first catalyst-containing stage;maintaining the one or more sequential catalyst-containing stages underconditions sufficient to convert hydrogen and oxygen to hydrogenperoxide as the downstream feedstream is fed therethrough; andrecovering hydrogen peroxide from a reactor effluent, the molar ratio ofoxygen to hydrogen within each stage of the multi-stage reactorexceeding the overall molar feed ratio of oxygen to hydrogen utilizedthroughout the method.
 16. A method as defined in claim 15, wherein themolar ratio of oxygen to hydrogen introduced into the first conversionzone is at least about
 3. 17. A method as defined in claim 15, whereinthe overall feed ratio of oxygen to hydrogen utilized throughout themethod is from about 1 to about 1.67.
 18. A method for the directcatalytic conversion of hydrogen and oxygen to hydrogen peroxide,comprising: introducing a feedstream comprising oxygen, hydrogen, and aliquid media into a first catalytic conversion zone of a multi-stagecatalytic reactor, the reactor being comprised of a plurality ofserially connected catalytic conversion zones and a catalyst forconverting hydrogen and oxygen to hydrogen peroxide, the feedstreamhaving an initial molar ratio of oxygen to hydrogen of at least about1.5; converting hydrogen and oxygen to hydrogen peroxide in each of thecatalytic conversion zones, a portion of the oxygen in the initialfeedstream being consumed in each of the catalytic conversion zones suchthat each successive catalytic conversion zone includes less oxygen thana preceding catalytic conversion zone; introducing supplemental hydrogeninto one or more catalyst conversion zones downstream from the firstcatalytic conversion zone in order to lower the molar ratio of oxygen tohydrogen in the one or more downstream catalyst conversion zones to aratio that is closer to the initial molar ratio in the first catalyticconversion zone compared to that of an effluent from a precedingcatalyst conversion zone, the molar ratio of oxygen to hydrogen withineach stage of the multi-stage reactor exceeding the overall molar feedratio of oxygen to hydrogen utilized throughout the method.
 19. A methodas defined in claim 18, wherein the molar ratio of oxygen to hydrogenintroduced into the first conversion zone is at least about
 3. 20. Amethod as defined in claim 18, wherein the overall feed ratio of oxygento hydrogen utilized throughout the method is from about 1 to about1.67.